revert "mzscheme" and "mred" collection versions

and turn off automatic "mzscheme" version dependency for
 package .plt files

collects/mred/info.rkt

@@ -1,4 +1,4 @@
 #lang setup/infotab
 
-(define version '(510))
+(define version '(400))
 (define post-install-collection "installer.rkt")

collects/mzscheme/info.rkt

@@ -1,6 +1,6 @@
 #lang setup/infotab
 
-(define version '(510))
+(define version '(400))
 
 (define post-install-collection "installer.rkt")
 

collects/setup/pack.rkt

@@ -280,6 +280,11 @@
                              r))
                           (list r v))
                         (list r null)))))
+                requires
+                ;; Packer used to automatically include "mzscheme"
+                ;; dependency, but we've conlcuded that dependencies
+                ;; aren't typically useful.
+                #;
                 (cons '("mzscheme") requires))
            #:conflicts conflicts
            #:at-plt-home? at-plt-home?